Analysis: 1981 to 2006
Epidemiology of feline uroliths: 1981-2002
Carl A. Osborne, DVM, PhD, Dipl. ACVIM
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In 1981, calcium oxalate (Table 2) was detected in only 2 percent of feline uroliths submitted to the Minnesota Urolith Center,
whereas struvite (Figure 1) was detected in 78 percent. However, beginning in the mid-1980s, a dramatic increase in the frequency
of calcium oxalate uroliths occurred in association with a decrease in the frequency of struvite uroliths (Figure 2). From
1994 to 2002, approximately 55 percent of the feline uroliths submitted to the Minnesota Urolith Center were composed of calcium
oxalate, while only 33 percent were composed of struvite. During this period, the decline in appearance of naturally occurring
struvite uroliths associated with a reciprocal increase in calcium oxalate uroliths may have been associated with:
1) The widespread use of a calculolytic diet designed to dissolve struvite uroliths
2) Modification of maintenance and prevention diets to minimize struvite crystalluria (some dietary risk factors that decrease
the risk of struvite uroliths increase the risk of calcium oxalate uroliths)
3) Inconsistent follow-up evaluation of efficacy of dietary management protocols by urinalysis.
Epidemiology of feline uroliths: 2003-2005
Jody P. Lulich, DVM, PhD, Dipl. ACVIM
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In 2003, the frequency of calcium oxalate uroliths declined to 47 percent, while the frequency of struvite uroliths increased
to 42 percent (Table 2). During 2004, the number of struvite uroliths (44.9 percent) submitted to the Minnesota Urolith Center
nudged past those containing calcium oxalate (44.3 percent). In 2005, the number of struvite uroliths (48.1 percent) surpassed
those containing calcium oxalate (40.6 percent) in frequency of occurrence.
Epidemiology of feline uroliths: 2006
Of 10,093 feline uroliths submitted to the Minnesota Urolith Center in 2006, 5,001 (50 percent) were struvite, and 3,914 (39
percent) were calcium oxalate (Table 1).
The progressive decrease in occurrence of naturally occurring calcium oxalate uroliths during the past four years may be associated
with:
- Reformulation of adult maintenance diets to minimize risk factors for calcium oxalate crystalluria.
- Improvements in formulation of therapeutic diets designed to reduce risk factors for calcium oxalate uroliths.
- Increased use of therapeutic diets designed to reduce risk factors for calcium oxalate uroliths.
The increase in appearance of naturally occurring struvite uroliths during the past four years may be associated with the
reciprocal relationship between some dietary risk factors for calcium oxalate and struvite uroliths. For example, diets that
reduce urine acidity and provide adequate quantities of magnesium reduce the risk of calcium oxalate urolith formation, but
increase the risk of struvite (magnesium ammonium phosphate) urolith formation.
Table 1 Mineral composition of 10,093 feline uroliths and 551 urethral plugs submitted to the Minnesota Urolith Center during
2006
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Figure 2: A 3-year-old domestic shorthair cat after digital manipulation of the distal urethra and manual compression of the
urinary bladder. Fragments of a struvite-matrix urethral plug that had occluded the urethral lumen can be seen on the microscope
slide.
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